The invention relates to scanning devices for capturing information, for example images from paper carriers, and is particularly concerned with scanning devices for capturing information on financial instruments such as banknotes of various types.
Various scanning devices for capturing information on paper image carriers are known. The most well known devices are hand-held scanners for reading bar codes, e.g. one patented under USSR Inventor""s Certificate No. 1837334. That device contains a light source, a converging lens, an aperture diaphragm and diaphragm-coupled light receiver, all optically coaxial. A spherical lens is mounted between the scanned carrier and the aperture diaphragm. Such device may have the form of a ballpoint pen-like rod and be of a fairly simple design. The functionality of such a device, however, is limited to reading bar codes, its accuracy, resolution and operation speed being insufficient for other purposes. Other hand-held apparatusesxe2x80x94more sophisticated in design and having expanded functionalitiesxe2x80x94are also known (e.g. U.S. Pat. No. 5,349,172, U.S. Pat. No. 5,354,977, WO 94/19766 and WO 94/19764). Those devices use LED arrays to illuminate the carrier scanned and CCD arrays to take in reflected signals. Such devices, however, do not have sufficient functionality for scanning in large amounts of information when necessary.
Also known are desk-top scanning devices for capturing images and printed information. Such devices contain an optical unit comprising a light source, a light guide, a focusing and/or filtering optical element system, a light receiver and an A-D converter processing signals from the light receiver (e.g. Russian Federation Patent No. 2032217 and U.S. Pat. No. 5,295,196).
The deficiencies of known devices consist in their design complexity and the illuminator""s excessive power consumption. The complexity of design is primarily the result of the sophisticated optical system which uses lenses, mirrors, etc. as focusing elements which are challenging in manufacture and require precise adjustment for correct operation of the device. Moreover, in order to obtain reflected luminous flux of sufficient intensity, a great amount of light energy is required to illuminate the information carrier.
The objective of this invention is the development of a scanning device, which is simple in design, provides high performance and high speed of operation at a low power of illumination to capture images on transported carriers, for example paper or plastics, and in particular security documents such as credit cards, identification cards and banknotes carried on a transport system, such as a banknote processing machine.
In accordance with the present invention, we provide a scanning device for capturing images, which contains an optical unit comprising a light source, a light guide, and a light receiver, wherein the light guide comprises a substantially parallel sided, transparent member, the member having opposite ends extending between the parallel sides, one of the ends facing the light source and extending non-orthogonally between the parallel sides, the other end facing the image to be scanned in use, whereby light from the light source enters the light guide through the one end, is directed onto the image after passing out of the other end, is reflected back into the light guide and then directed by the light guide towards the light receiver.
The use of a light guide of this form concentrates light from the light source on to the carrier, thus enabling relatively weak sources to be used while at the same time providing a simple way of separating the transmitted and received light (and corresponding transmitting and receiving apparatuses) in a compact manner.